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Inside Imhotep

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20/07/2015

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Imhotep, on Comet 67P/Churyumov-Gerasimenko’s large lobe, is one of the most geologically diverse regions observed by Rosetta. This blog post presents the results of a new paper by Anne-Thérèse Auger from the Laboratoire d’Astrophysique de Marseille (LAM, France) et al, which describes Imhotep’s key features and discusses possible scenarios for this region’s evolution. The post was prepared with inputs from Anne-Thérèse and co-author Olivier Groussin, also from LAM.

Click for large version. All images: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Imhotep is located close to the comet’s equator and is relatively flat compared to the overall shape of the nucleus. It caught the attention of scientists on the approach to the comet with its broad smooth area, covering about 0.8 square km, standing out in the first close images of this region. Within this intriguing area, a variety of diverse features can be found. This diverse geomorphology holds fundamental clues to understanding the cometary processes that lead to the formation of the surface as we see it today, and also provides insights for the underlying and possibly primordial structure of the comet.

Anaglyph image of part of the Imhotep region on the large lobe of Comet 67P/Churyumov–Gerasimenko. To best enjoy this view, use red–green/blue 3D glasses. The image was created from two OSIRIS narrow-angle camera images acquired on 22 November 2014 from a distance of 31 km from the comet centre. The image scale is 56 cm/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; acknowledgment: D. Romeuf (University Claude Bernard Lyon 1, France)

The graphic below maps the geomorphology of the region, indicating the different types of features identified in Imhotep. The context image at the start of this post showcases some examples of each of these features. Short descriptions follow.

Geological mapping of the Imhotep region on Comet 67P/Churyumov–Gerasimenko.Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Smooth terrainsSmooth terrains cover about one-third of Imhotep and are located in the gravitational lows. High-resolution (30 cm/pixel) images show that it comprises fine-grained material with a size of up to a few tens of centimetres for the largest grains. As seen elsewhere on the comet, the thickness of the dust seems to vary, with the underlying surface revealed in places. Within the smooth terrains a number of curvilinear features are seen, spanning hundreds of metres to a km in length. In some places they cross the interface between smooth and more consolidated terrain, suggesting a continuation of the consolidated terrain below.

Close ups of smooth, fine-grained material in the Imhotep region on Comet 67P/Churyumov–Gerasimenko. The insets on the right-hand side correspond to the boxes outlined in the left-hand image. A close-up of part of a long, curvilinear feature is also shown. The image was taken with Rosetta’s OSIRIS narrow-angle camera on 5 October 2014. The image scale is 34 cm/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The smooth terrains are considered relatively undisturbed areas that evolve slowly and where material has time to settle and accumulate. Anne-Thérèse and colleagues propose that the fine material originates from the cliffs on the border of the basins where mass wasting occurs. It is then transported by gravity downslope to a flat surface. The wideness of the smooth area can be explained by the progressive retreat of the cliffs over a long time, probably some tens to hundreds of perihelion passages, meaning that the more distant the fine material is from the cliff, the older the deposit is. “Airfall” deposits as a result of activity elsewhere on the comet may also contribute to a small fraction of the dust observed here.

‘Rocky’ terrainsThe term ‘rocky’ is used as way to distinguish this terrain from the smooth terrains; in reality, the comet’s density is very low, some 470 kg/m^3 , and it is extremely porous. These ‘rocky’ terrains consist of consolidated material that is exposed at the periphery of Imhotep. They are the sites of erosion, as emphasized by the large numbers of boulders and debris seen close to these outcrops. The erosion observed along the exposed walls is likely triggered by the sublimation of ices, controlled by gravity and exacerbated by fractures.

Accumulation basins identified within the boundary of Imhotep. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Accumulation basinsAccumulation basins dominate Imhotep, and are defined as areas where fine material and boulders seem to accumulate preferentially. Six basins have been suggested within Imhotep, covering about two-thirds of this region (other possible accumulation basins lie just outside the defined boundary). The near-circular appearance of the majority of the basins is interpreted as the surface expression of large primordial voids in the nucleus that existed since the comet’s formation. Over time, the overlying surface was weakened by erosion and fracturing, and it eventually collapsed, with erosion over time widening the basin and filling it in with debris. Basin F is observed to be slightly different in that it is extensively fractured, with the fractures pointing towards its interior. Since this pattern is not a feature associated with collapse, it must have formed or been modified in some other way, perhaps by impact or associated with activity, perhaps even by a gas bubble rising from the interior (as already proposed by other scientists for Comet 9P/Tempel 1).

A range of features can be seen in this image, including curvilinear features in the smooth material (left) and terraces close to a basin-like feature (centre). To the top, a number of quasi-circular features can be seen. The image was acquired with Rosetta’s OSIRIS narrow-angle camera on 5 September 2014 from a distance of 43.5 km from the comet centre. The image scale is 80 cm/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

TerracesTerraces are seen in various locations on the comet and strongly suggest internal layering (a topic that will be discussed in more detail in a future paper). The layers in Imhotep have a relatively constant thickness of a few metres, implying a repetitive process, perhaps by compaction of successive deposits of material. The terraces highlighted at basin F are extensively fractured, meaning that the layers formed first, before the basin, and before the fracturing. As such they may be pointing to processes relating to the formation of the comet itself, or to an ancient evolutionary process.

Colour-composite image focusing on bright and bluer patches in the Imhotep region on Comet 67P/Churyumov–Gerasimenko. The image at right shows a zoom into the region indicated in the left-hand image. The composite comprises images taken with the blue (480 nm), green (536 nm) and orange (649 nm) filters of Rosetta’s OSIRIS narrow-angle camera on 5 September 2014, from a distance of 43 km from the comet centre. The image scale is 81 cm/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Bright patchesA few bright patches are seen on exposed walls. They appear bluer than the average colour of the comet in colour-composite images and suggest the presence of ice. If they are confirmed as water-ice, these could be some of the youngest areas on the comet.

Round featuresGroups of quasi-circular features like these have only been seen so far in the Imhotep region on Comet 67P/C-G – around 70 have been identified measuring between 2 m and 59 m across. They have a rim and at their top either a depression or a mesa of fine material that sometime seems to bulge above the rim. Many of these features appear to be stacked on top of one another. Their formation mechanism is not clear but one scenario is that they represent ancient degassing conduits that were once exposed, subsequently covered over by dust, and are now being revealed by differential erosion of the overlying layers. Interestingly, roundish features with a similar morphology were also observed on Comet 9P/Tempel 1.

Recently illuminated regions in the south of the Imhotep region on the large lobe of Comet 67P/Churyumov-Gerasimenko reveal round features similar to those seen in the centre of the same region. The image was taken with Rosetta’s OSIRIS narrow-angle camera on 31 October 2014 from a distance of 33 km from the comet centre. The image scale is 63 cm/pixel. Credits:ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

BouldersSome 2207 boulders have been counted in Imhotep, with sizes from 2 m (the lowest limit of the observations) to 90 m. They are mostly located at the bottom of slopes and are associated with mass-wasting of more consolidated terrains. A number of large boulders (including the famous Cheops boulder) lie isolated towards the centre of the smooth region. With a size of tens of metres, it is unlikely that they are airfall deposits. Anne-Thérèse’s team suggest that the boulders are the remnants of a previous mass wasting event at the foot of an earlier cliff, when the basins were less wide. The boulders have appeared to slightly sink over time, as material accumulated around them.

Evolution of ImhotepBased on this overview of the geomorphology of Imhotep and of the processes thought to be responsible for its landscape, Anne-Thérèse’s team propose a scenario for the formation and evolution of this region.

They suggest that first the basins are formed through collapse of large pre-existing cavities in the comet nucleus. Over time these basins are eroded through sublimation of ices exposed in their walls and interiors, enlarging their rims and infilling their interiors with boulders and fine-grained material. The degradation of boulders and further erosion from mass-wasting, combined with airfall deposits, leads to the accumulation of smooth material in gravitational lows. At the same time, differential erosion of the surface may reveal underlying features such as the possible ancient conduits.

“There are still a lot of mysteries, but now that we are approaching perihelion we will be looking out for any changes on the surface, which will help us understand how this region evolves today,” concludes Anne-Thérèse.

Discussion: 81 comments

I stumbled over “it must have formed been modified in some over way”. I guess, it should have said “it must have formed or been modified in some other way”?

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emilyPosted on 20/07/2015 at 19:11

Thanks Gerald!

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Bill HarrisPosted on 20/07/2015 at 19:24

Excellent paper, and a very good outline of the geomorphic processes at work on 67P.

–Bill

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Robin ShermanPosted on 20/07/2015 at 20:10

Absolutely fascinating Emily. Thanks to the contributors and the OSIRIS team for explaining these processes.

One thing that is immediately obvious from these NAC images compared to the lovely NAVCAM images, is the vast amount of rubble and debris littering the surface. I certainly did not suspect there were such huge amounts of surface erosion going on.

The other surprise is the flat plains of the region, we thought were “dust” covered. From the text and images it seems they are covered in pebbles and stones of quite large size ~50 – 100cm in places. I envisioned this coarseness of the terrain to be lumps and bumps in the surface terrain, like tiny moguls. The devil is in the detail.

Other than those points, I think as citizen scientists looking on, we did quite well with our speculations and educated guesses. The number of basins and their suggested formation process, suggests that voids within the comet structure are not uncommon and thinking of the Seth region, frequent. It is to be hoped that eventually CONSERT will be able to confirm this theory. No mention was made of the possibility of the voids being gas filled or material sublimating to fill a vacuum. One would imagine they would all be pressurised to some degree until cracks form allowing gas to escape to the surface, like in the area of “toadstools”.

I liked the explanation for the “toadstool” features. I got as far as escaping gas vents, creating something like mud volcanos, the erosion of material to leave the below surface tube behind never occurred to me though. That lack of appreciation of the extent of erosion processes again.

Slightly disappointed that the actual properties and numbers rule out largely the ice phase change scenario as a subsurface source of energy. I did think it might be dependent upon the thermal properties of the cometary material. It seems solar thermal energy only reaches a metre or two at most below the surface, so it takes an awful long time for energy to seep down far enough to encourage pressurised gas bubbles below the surface, but its good to see it is considered a viable process, if only a less frequent one.

This paper has certainly gone a long way towards answering a lot of my pre and post comet rendezvous questions.

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A. CooperPosted on 21/07/2015 at 00:42

There are three bright boulders at the top of the main hi-res picture with the orange letters on it. These three boulders are just below the shadow cast by the perfectly circular crater. The middle one looks uncannily like the three sitting on the surface of Aker, which were the subject of a Rosetta blog post a couple of months back.

The rock in question has a characteristic scoop taken out of it which looks as if it might run the length of the rock. Although there may be sizing issues (is it somewhat bigger?) it looks identical to one of the three on Aker. It’s as if the two rocks could be clicked together, end to end and form one continuous elongated rock, even though they are now 2 or 3 km apart.

Seeing as Marco and I have been saying since February 2015 that Imhotep is the tray left by a missing slab, this twinning of two disparate rocks isn’t quite so far-fetched as is may seem. When the Imhotep slab was lost due to spin-up of 67P, collateral rocks would’ve been ejected at suborbital speed by getting a chance backward kick down the rotation plane. We’ve already cited one definitive example of this on Site A several times before. For these two rocks on Imhotep and Aker to have any chance of a plausible link, they would have to align to within perhaps 100 metres of the rotation plane. Looking at the DLR rotating comet on their website, it appears that this may well be the case although it’s a grainy shape model. In other words, if you draw a line from the rock on Imhotep round to Aker while keeping it parallel to the rotation plane, that line will pass very close to the three closely spaced rocks on Aker which include the ‘twin’.

The other two rocks in the trio on Imhotep resemble the remaining two on Aker as well but only in a general way. I’m not saying all six make three sets of twins. However, the general similarities of both trios, their alignment along the rotation plane and the possible twinning of two of them lends a degree of weight to the argument that the trio in Aker came from this location in Imhotep. Add to that the fact that the three on Aker appear orphaned, set as they are in a smoother landscape and the argument strengthens. Furthermore, I’ve not seen any other such characteristically scooped-out rocks like these two in all my hours of poring over the photos.

I made a comment on the ‘three rocks’ post saying they may have come from Aten or even Imhotep due to the process of rotation plane travel described above. These two ‘twins’ are interesting candidates but I wouldn’t present them with the same certainty as I have for the Site A rocks. On Site A, the rocks and their matching seating points are linked along the rotation plane. Here we have no discernible seating.

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MarcoPosted on 21/07/2015 at 12:20

The take home message is that slab removal as an explanation for Imhotep explains a lot of the morphological surface differences with other areas. The related debris fields of boulders is explained from the collateral surface fractures in the removal of the Imhotep slab. The fractured terraces are a dead giveaway that a large mass wasting event occurred here, exposing the surface and near subsurface layering. The fact that Imhotep is so large and yet so flat is a big hint of a removal and fracture along a boundary between layers, like dragging a scoop picking off a layer of lasagne.
Of course the evidence doesn’t rule out erosion, but erosion just doesn’t make sense for the flatness at any scale. Flatness requires static liquid or liquid-like processes. Erosion gouges out rough shapes from flatness.
Additionally, the boulders are quite obviously fractured, transported, landed and then stayed put without any erosion at all. This is why Andrew, quite rightly looks at matching features. The attributes of these boulders, as well as lack of erosion, means we can try to piece together boulders back to where they were originally part of the crust of 67P.

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A. CooperPosted on 23/07/2015 at 02:20

Moving on from the ‘twinned boulders’ comment, above, but focussing on the same principle of backwards rotation plane travel. One would expect a slight bias of debris on east-facing slopes of any humps or dips in the otherwise flat, dusty area in the middle of Imhotep. This is because the backwards travel of these suborbital rocks is directly westward. Any tipped-up eastward-facing terrain will catch more rock debris than any similarly inclined west-facing slope. It would likely only be a very slight difference because the humps and dips are gentle across the plain of Imhotep. This is in contrast to the Nut region at the opposite end of the comet that sticks up markedly, faces directly east and is littered with rocks.

Looking at the hi-res photo in the article (with the orange letters) you can see two main clumps of boulders on ‘D’, the flat area. There is indeed a preponderance of debris on the east-facing slopes of the undulations (as discerned by the slightly darker shading). The equator runs in line with the ‘B’ to ‘E’ line but displaced a tad north so that it goes through the Cheops rock (largest rock in middle of the dusty plain). The equator is the xy rotation plane. Rotation planes for rocks north or south of the equator are parallel to the xy rotation plane. They all run at 90° to the ‘North’ arrow so they are like latitude lines. Direction of comet rotation is top left to bottom right so the suborbital rocks are going the opposite way (or, to be precise, travelling the same way but more slowly).

Furthermore, the small scree-like debris that surrounds each large boulder or sub-group of medium boulders is biased towards the west. This is consistent with the larger boulders landing and the scree that was riding on them being sent further on westward. The boulder landed and the scree slid off the top, landing in a line a hundred metres or so long, further west down the rotation plane. This has been documented already on the stretch theory blog for the two rocks on Site A. Their scree field is spread entirely westward of their landing position and is in line with the rotation plane.

Area E is the actual source of all the debris described above. It’s the hinge against which the missing slab slid and wedged before lifting up and grinding all the rocks out. It’s clearly a site of more aggressive excavation and it’s exactly where you would expect it to be: at the eastern end of the slab. This is why it’s a source of intense sublimation. The ‘comet fart’ jet is emanating from this area (my interpretation of Mattias Malmer’s study of the jet location). It’s most probably jetting from the now-exposed fracture plane below the top stratum.

It’s also of note that the two groups of boulders are exactly in line with the presumed deepest and most disturbed part of the excavated hinge. The presumption is made on the basis of 1) the slightly darker (deeper?) area just to the left of the big white boulder that’s poking out and 2) the area of in situ boulders (more disturbance?) just above the dark area. The two groups out on the dusty plain are exactly in line with this area in the sense that the width of the rotation plane ‘corridor’ they floated down is the same width as this area So there’s a corridor of width 500 metres and at one end there are boulders sitting neatly within it while at the other end the two corridor perimeter lines kiss the north and south tips of the disturbed patch.

Note also that the in situ rocks in the disturbed hinge area have a remarkably similar shape, size distribution and brightness to their supposed cousins out on the dusty plain.

This trait can even be seen at higher resolution within the two sets, that is, within the in situ hinge rocks and the dusty plain rocks. The northern group of in situ rocks match the northern group out on the plain in terms of their size distribution and you can run a rotation plane line through both groups. And as for the three large, isolated boulders out on the plain including Cheops, they line up with the giant boulder poking out of the hinge area. If you draw a rotation plane line through the hinge boulder it runs plumb through Cheops. The hinge boulder has what is very likely a large gouge out of its tip. The three boulders on the plain would fit nicely into it. So I’m proposing it’s no small possibility that Cheops is a chip off this boulder, broken away when the Imhotep slab hinged up.

The boulders discussed above, their scree fields and and their source are elegantly explained by the collateral effects of stretch theory: a slab being ejected from this area just prior to or during stretch. Instead of taking one hundred perihelions, it would have taken somewhere around 100 minutes.

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A.CooperPosted on 24/07/2015 at 18:40

In my last comment regarding the link between sets of rocks in the gouged-out hinge and out on the dusty plain, I was aware that there was a distinct gap between Cheops and a clump of three boulders some way to the south. Those three boulders also have six discernible smaller rocks, four westward, one in line and one eastward.

So what of this dearth of rocks in the middle? If all these rocks are supposed to have been displaced from the same deeply excavated area and dumped on the dusty plain (area D) why would one part of the excavation withhold its rocks? Having read the paper (the PDF wasn’t downloading for me before) I believe I have the answer. The gravitationally lowest point on Imhotep is marked by an ‘x’ in the paper. It’s almost exactly between the D and the E on the hi res photo in this Rosetta blog post- a small flatish area surrounded by what they call “roundish features”. That is a little to the west of the slightly darker patch (next to the giant boulder) that I had suggested as being the lowest. The reason I had suggested this darker patch is that it’s nestled against the fracture plane between the stratum layer that supplied the rocks for the groups on the plain and the next stratum down. You can see the fracture plane arcing all the way from the thick line of shadow, north of the letter E, round under the rocky stratum, across the bottom (and top) of the giant boulder and round to the arced formation below the orange ‘E’. The dark area would therefore be the gouged top portion of the second stratum down. The ‘x’ proves that this second stratum was gouged even deeper to the west.

The fact that there are two stratum layers involved in the gouged hinge is key to the north-south distribution of the rocks out on the plain. The upper stratum is a conglomerate of boulders that supplied the suborbital rocks (the authors suggest it’s a ‘conglomerate’, my previous comments implied it was so). The lower stratum, in contrast, appears not to be a conglomerate but does contain evidence of intense outgassing. This would be consistent with a) heat generation by the slab grinding on the hinge and b) sudden gas escape from the newly breached join between the top two fracture planes (because the body lobe was stretching somewhat due to spin-up and generating heat within as a result). This portion of the hinge clearly had no rocks to send back down the rotation plane due to its not being a conglomerate and/or because it swamped them with slurry from the outgassing below the uplifting slab. The authors don’t mention slurry- it’s quite obviously pooled in that lowest part (the ‘x’) to the west of the main line of ’roundish features’ which are, essentially, gas/slurry dykes.

The main concentration of roundish features follows a north-south line in the top of the second stratum that would be consistent with the north-south orientation of the hinge ‘axle’. Although the roundish feature area had no rocks to supply, this north-south orientation explains the north-south nature of the rock distribution on the dusty plain because the axle was where the greatest amount of grinding out occurred. The axle, (the rock source) was therefore also along a north-south line with a dearth of rocks in its middle area.

If you were to draw two lines along the rotation plane, one kissing the northernmost roundish feature and the other kissing the southernmost, those two lines define a corridor that runs straight through the rock-free portion of the dusty plain. They kiss Cheops in the north and the clump of three in the south. This is why there are no rocks in that portion of the dusty plain- the area of roundish features that is forward along the corridor from this rock-free zone, had no rocks to supply.

Incidentally, if you extend the N-S hinge axle that supplied the rocks, you find a possible source for the southernmost clump of dusty plain rocks. It’s an alcove 200 metres south of the ‘E’. It has a similarly large boulder perched on its eastern lip (see boulder schematic).

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MarcoPosted on 24/07/2015 at 09:27

Regarding the contrast between sublimation led surface processing (theory) with rotational led surface fracturing (theory) it is about time for a differential diagnosis between the two. Despite regular iinterjecting deas that “lots of different processes drive surface change”, the evidence of slab removal is completely incompatible with the erosion of cliffs from the edges and surface. Erosion would remove evidence of where boulders were seated to cliffs, in the same way that a wave washes away footprints in the sand.
This is not a trivial problem, as, if we are expecting surface erosion, we could not easily interpret how things look different under different lighting, while even tiny features noted by one angle should be assumed to still be there even if a different angle completely washes it out, when we assume no erosion.
Repeated measurements at high resolution under different lighting conditions pre and post perihelion will prove this issue one way or another. All circumstantial evidence seems to point to a very static surface that is resilient to change even under harsh thermal stress of solar radiation.

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A.CooperPosted on 24/07/2015 at 23:00

Marco

I agree a differential diagnosis should be carried out. The trouble is that if one isn’t open to the possibility of stretch theory, one isn’t going to notice the multitude of stretch theory signatures- or even know what they should be. Rotation plane travel of boulders is two stages further on from the concept of stretch. That’s because slab removal is a collateral effect of stretch and slabs shedding rocks from their lifting/hinging undersides is a collateral effect of slab removal. No one is going to look up and down the rotation plane for these rock-travel signatures if they are unaware even of their possible existence.

As for your mention of matching rocks to their exact sources via matches, I tried looking for matches between Cheops and the chipped, giant boulder in the “conglomerate” (the authors’ suggested term with which I wholly agree), up at the hinge. The resolution isn’t good enough for what would be small-scale undulating matches on a bright surface, as opposed to large-scale deep-cut matches on a darker surface for the Site A rocks. However, both Cheops and the giant boulder exhibit a general appearance of having something akin to square-conchoidal fractures. That would be a conchoidal fracture that’s got quasi square edges as opposed to curved edges- rather like a concave version of a tortoise shell. Cheops and the boulder exhibit three of these in a row but the shapes aren’t exactly the same, at least not in their current, fuzzy form. This is in contrast to the absolute certainty for one rock on Site A and near-certainty for one other. I might get further with a trawl through the other Imhotep pics taken on February 14th 2015 at 6 km altitude. Although I couldn’t see any definitive matches, the character of the two fractured boulders is strikingly similar. And of course, they line up along the rotation plane.

But the reason for saying all the above is as a lead-in for another missed signature of giant slab removal because while analysing the giant boulder, I realised I had been looking at it without seeing.

You just wouldn’t interpret the following evidence as being a signature for a giant slab hinging up if you hadn’t already entertained the notion of slabs hinging up due to spin-up and stretch. In fact, you would put all the following traits down to shear random effects of mass wasting via sublimation.

The manner in which the tip of the giant boulder has been ground off provides extra evidence for the Imhotep missing slab grinding its eastern end round in the hinge. The back end of the Imhotep slab was lifted up from the western end of Imhotep so the grinding movement in the hinge at the eastern end, against the giant boulder, was from east to west. The fact that the giant boulder has had the top of its tip ground off is consistent with this grinding direction. I’d go further: it appears that the giant boulder has been pressed down hard into the matrix below. The evidence for this is a moulded surface formation below the boulder that matches its profile perfectly (that’s what I had missed). It also has two or three roughly east-west striations on its top surface, running east from the ground-off tip. I would suggest that only the tip was protruding from the conglomerate at one point whereupon the grinding slab caught it, pressed it down hard into the matrix below and chipped the end off in the process. When the Imhotep slab lifted off for good after hinging, the giant boulder popped back up again, hence the big gap/shadow under it and its back scrubbed almost free of rocks. The striations would be where the slab ‘tried’ to get a grip before it actually did so. The matching, moulded matrix below it remained as testament to the pressing-down event.

Remarkably, if you push the boulder back down, in your mind’s eye, into the mould it made when pressed down, the ends of the striations on its back meet up with the end of the mould line below (I had missed that too). That implies one big long scraping motion across the boulder- but only when pressed down. And now that it’s popped back up, it bears an uncanny resemblance to a flint that’s been almost worked free of a chalk face via a rocking motion (apologies in advance to Harvey).

As I often say, the evidence is right there in front of us. I can look at a feature dozens of times before I finally see the wood for the trees. Once you see it, you can’t ‘unsee’ it. It’s definitely there and very obviously telling a story.

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MarcoPosted on 27/07/2015 at 09:51

A.Cooper
The whole point of a (continuing) differential diagnosis is to predict collateral effects that you would expect with one, than the other, and then see how many “symptoms” match each diagnosis as new information comes to bear.
I think the problem is that there is no explicit predictions for sublimation led surface processing, except in the dynamic case where we would have to wait for after perihelion to notice whether and where erosion is *Actually* occurring rather than presumed eroded features based on their shape.
In medical differential diagnosis, the equivalent is a catch all diagnosis like “a virus” ignoring possible alternative specific diseases or opportunities to define a new disease with particular features that don’t fit the mould of a typical virus.
I get tired of the comment that the chances of it not being a virus are very slim.

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originalJohnPosted on 21/07/2015 at 01:54

It would be refreshing for the investigators to sometimes include the alternative explanations they have considered for observed phenomena. Otherwise it looks as though they have only considered one. For example here, other ways in which rock might have been shaped, particularly into the ubiquitous circular shape.

It would also be helpful to see some additional evidence, other than the density figure, that the rock is indeed porous, particularly with regard to the speculated large internal cavities that the postulated surface morphology mechanism depends on.

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ianw16Posted on 21/07/2015 at 14:01

@originaljohn
Perhaps you’d like to summarise the “alternative” explanations, and the evidence gathered at this, and other comets, that might make them worth considering.
As for the porosity; well, first you need to *explain away* the density figure. There is no scientifically valid way of doing that. Electrostatic repulsion woo doesn’t work, as has been shown, and would be noticed. So the density, for scientists and the scientifically literate, is a done deal.
The low density nature of comets was confirmed by the Deep Impact mission, which excavated a lot of water ice and dust. The crater it excavated is not consistent with a dense, consolidated surface.
Nor, indeed was any sign of a giant electric discharge or double flash noticed (except in the eyes of EU advocates).
SWIFT data confirmed that.
However, yet again, EU proponents see what they want to see in order to carry on the delusion, whilst consistently ignoring the mountains of evidence which shows it to be nonsense.
I’ll reiterate what I’m sure I’ve said before: there isn’t a single piece of evidence in favour of this “electric rock” nonsense.

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Sovereign SlavePosted on 22/07/2015 at 15:33

LOL, yes, why ever consider “alternative” explanations, for goodness sake? How unscientific. But despite your always predictable, votarient comments Ian, sublimation woo and twaddle simply can’t explain or model much at all when it comes to the features and activities encountered on P67. No cause for other considerations, though, or to question, or to peak outside your comfortable belief system.

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ianw16Posted on 23/07/2015 at 12:07

So like I said; what are these “alternative” explanations, and where is the evidence for them?
For instance, what is the evidence for this, or any other comet being made of rock? Where is the evidence for electrical activity on this or any other comet? How do you explain the density of this and every other comet where such measurements have been made? Where is the water and CO2 coming from? Require a billion to trillion fold increase in the solar wind? Where is the evidence for that?
Sublimation doesn’t work? How come? Please explain why not? What is the evidence?
No hand waving, just evidence and real science please.
Like I said, the electric rock nonsense has not a single line of evidence to support it. All based on pareidolia.
Very scientific.

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HarveyPosted on 23/07/2015 at 22:07

Sublimation has a huge amount of detailed mechanism explaining to do, that’s for sure.
But at a crude overall level it works. The species degassed, the temperature, the energy input required to generate that much gas etc etc all work.
In contrast there is no understandable, coherent model of these supposed ‘alternative processes’ AT ALL. Not at the most primitive, simplistic level, let alone at a numerical level. No one has ever been able to respond to the simplest possible questions about how thie discharge idea can work.
When an alternative that obeys the basic laws of physics and fits the gross observations is proposed, everyone will be very happy to consider it.
If such an alternative could be found – and none exists right now – it would then have to address all the same questions about how exactly it leads to the bizarre and complex morphology we see on 67P; none of these frankly ridiculous alternatives is one jot further forward than sublimation in doing that of course.
What really amuses me is the complete inversion of reality of your final sentence. We have no ‘belief system’; everything and anything in science is always up for grabs, stands just as ling as the evidence supports it and not a second longer.
We don’t do belief, we do *evidence*, and we do *physics*, unlike the alternatives.

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originalJohnPosted on 24/07/2015 at 18:43

You don’t read the replies Harvey. You have had numerous fully coherent explanations of how the discharge works. You have had numerous fully coherent explanations of the combustion process I proposed. There has been no evidence from this mission to discount them. All you do is invent figures which display your lack of understanding of the environment and its possibilities. And you continually regurgitate the ice sublimation hypothesis which has no evidence as yet to confirm it. It is simply the favoured consensus view and is indeed nothing but a belief.

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HarveyPosted on 27/07/2015 at 23:08

No, we have never had a coherent explanation here, let all me one that obeys the laws of physics and fits the observations.

At the crudest, simplest level, we have never had an explanation of how you run CW year long discharges off an insulator, never had a response to the capacitance/charge/current issues.

Sublimation has a stack of issues; but the so called alternatives don’t even get to first base to *start* trying to provide detailed explanations.

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KamalPosted on 28/07/2015 at 06:05

Sovereign slave, Re: any other alternatives.

Scientists tend to work with the most time-tested explanations so that they don’t have to redo their calculations and experiments all over again. You want them to work on developing their theory, then to come up with alternative theories, then to provide evidence to refute them, while you sit back and watch the fun.

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Sovereign SlavePosted on 30/07/2015 at 00:58

Hi Kamal
Exactly! Then we’d have the instant gratification of it all being presented in a neat and tidy package, no fuss no muss. And it’s not like they’re too busy or something.

But seriously, you make a good point, and highlight how cushy we have it with our armchair criticisms. Your comment does bring to mind Newton’s law of motion that a body in motion tends to stay in motion – guess it can apply to scientific investigations as well, with a reluctance to stray from the established direction of the motion and momentum.

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Sovereign SlavePosted on 26/07/2015 at 23:58

@Harvey & Ian
When I’m referring to alternative explanations, I’m not referring specifically to EU, but to ANY other alternatives. As both of you make abundantly clear, there are no other alternatives besides sublimation. There’s only one tool in the comet investigative toolbox, so any new finding or discovery is simply another nail for the sublimation hammer. This is beautifully illustrated by the ridiculous sinkhole proposition. Sublimation is the BELIEF that dictates the interpretations and subsequent speculations, no matter how far fetched or lacking in detail. So it’s nonsense to claim the scientific high ground in this matter. The fact is, sublimation is totally lacking in detailed explanations, but as long as its the unquestioned absolute unarguable belief, there will be no open scientific inquiry, or consideration that there may be other ways of looking at and interpreting the data, or developing “alternatives,” which should really be springing up and being presented from within the mainstream community, as originaljohns comment alludes to.

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ianw16Posted on 29/07/2015 at 20:15

Sorry, that’s nonsense. Ice has been shown to make up a good proportion of comets. Subsurface ice as well as water vapour in the coma, including close to the surface. The density of all comets measured rules out any other make up. Most certainly rock. Asteroids are rock. They are very different to comets. Even the ones in elliptical orbits.
So, first of all you have to come up with how ice is produced from an icy body without using sublimation.
Or you have to show that this isn’t an icy body, and explain away a shed load of evidence that says it is. So far there isn’t a scientifically valid hypothesis put forward to explain that.
Can’t explain the density, can’t explain the subsurface ice, can’t explain the lack of electrical activity that one particularly silly hypothesis calls for, etc, etc, etc.
Invoking unseen billion to trillion fold increases in the solar wind flux isn’t science, either.
It’s been nearly 30 years since the Halley encounter, 10 years since Tempel 1. I haven’t seen a single paper in the scientific literature putting forward a valid alternative hypothesis.
If there is one, let’s hear it, and, more importantly, let’s hear the evidence.

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Sovereign SlavePosted on 03/08/2015 at 15:17

There may or may not be ice, or an abundance of ice, on P67 and other comets, but regardless, the question is whether sublimation accounts for the coma’s and other activities/features observed with comets. But one interesting thing I’ve found in so many of the papers such as the ones your refer to, including on Tempel1, some of which I’ve read, is that the norm is for interpretations, speculations, beliefs, observations, conclusions, hypothesis, speculative models, wishful thinking, etc etc all seem to get mixed together and inevitably be presented as facts. For instance, take the double flash that took place when the Deep Impact impactor hit the surface of Tempel 1 (and yes, despite you saying the double flash didn’t happen, it did, it’s been discussed in some of the papers – you did read the papers you keep referring to, right? – and it was predicted by EU). So, a double flash was observed, but this of course does not make it a real fact. First, have to consider that it may have simply been visual display glitch or something else along those lines. It’s also helpful to get corroborative evidence that the flash took place. But by all accounts, it was determined with a good deal of certainty that a double flash did indeed take place. But here you run into one of countless problems with stating things with such absolute certainty like you do – most things fall on a probability percentile scale, and very few things hit 0% (absolutely not/could not be true) or 100% (absolutely is/could be true) relatively. Take again sinkholes. I doubt if anyone is 100% convinced that the pits on P67 are from sinkholes, even though this has now been presented as a fact, in this blog’s article title (at least in the title) and in popular media. Another thing presented as fact, that comets are primordial material from solar system origins. 100% absolute fact? No. It’s a presumption, a guess, and a belief. The fact is that we don’t know for certain what the origin of this comet is, we weren’t there to observe, record, take measurements, do experiments, etc. Yet everyone states it as fact. Getting back to the double flash, it has been agreed in the scientific community that it took place and is a fact, though an unexpected one by

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Sovereign SlavePosted on 03/08/2015 at 15:18

the mainstream community. Now to interpretation – EU interprets it as electrical in nature, mainstream that the first flash took place when the impactor hit the soft surface material, the second when it hit the harder underlying material. Both could be considered highly speculative, and highly speculative seems to apply to a huge amount of things that seem to be taken as facts in so many of these papers. Sublimation has huge issues, and it explains little of what we’ve discovered about P67, even though it’s touted as the major driving force behind most everything related to P67. And while large amounts of surface ice on P67 was expected, and it was a surprise it wasn’t present, this has now morphed into, “of course it’s not present, it would have been sublimated off long ago, the ice is now deeper.” Interpreting the Ceres lights bears this out as last I read, they’re doubting it’s ice now because it would need a replenished, continuous supply of it to maintain sublimation. (As an aside, if P67’s sublimation source is deeper and deeper each orbital trip, wouldn’t the sublimation begin later and later in the cycle as the comet approaches the sun each time?) So no, I don’t put the same stock in simply believing as fact everything that’s presented as fact in all those peer reviewed papers. As for alternatives, there will be none as long as none are considered, especially by the folks that hold and present all the data. As one scientist said, EU is a “non-starter,” and is dismissed out of hand. But it comes down to this: If the jets and other phenomena are due to sublimation, why does sublimation provide such a shocking lack of detail and explanation about these things? But if the jets and coma aren’t being created by sublimation, what are causing them?

A good image of a bright patch perhaps 70 metres across with other smaller bright patches nearby. You say Emily that they suggest the presence of ice. They could but they could also suggest other things. They could suggest local areas of electrical discharge combined with a surface combustion reaction. In either case a spectrum of water could be
detected at the surface, and without additional data no way of knowing if surface water signified ice below the surface
or was the product of a reaction at the surface.
You say ” if they are confirmed as water ice…” so clearly you have plans to collect further data. The simplest way of achieving that confirmation would be to measure the temperature of the bright patch.

If the bright patches are water ice the measured temperature will be below 0 deg Celsius, probably well below in this
case, let us say -50 to -100 deg Celsius. If on the other hand the bright patches are local electrical discharge/surface combustion sites the temperature measured will be above 0 deg Celsius, well above, let us say at least
400 deg Celsius, probably higher.

A difference therefore of at least 400 deg Celsius so absolutely no risk of confusing the two. The result would be clear and beyond dispute.

If your investigator colleagues, Emily, are confident that the bright patches are water ice let them go ahead and measure the temperature. Any scientist would be eager to do so, with the possibility of finally confirming their hypothesis. This would indeed be pioneering work.

I might add that a temperature below 0 deg Celsius could also indicate rock at that temperature, for example quartz which has that bright white appearance, but I would concede that that temperature combined with the bright (reflective) appearance would indicate water ice, if a spectral signature of
water was also detected.

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HarveyPosted on 24/07/2015 at 16:46

Please explain one very, very simple thing.

Every candidate material, be it ice, rock or hydrocarbon, is an insulator or very high resistivity material. We know from direct experimental evidence that it is an insulator or very high resistivity, because CONSERT 90MHz signals were received on paths through the core, albeit rather tangential to the surface. It’s very obviously not metallic.

How do you run a continuous discharge from an insulator?
RF discharges you can run on insulators, with a conductor behind it, but I think we might have noticed 67P broadcasting to the Universe, aside from what the RF power source would be, and the need still for a conductor.

Brief transient discharges can occur on insulators from surface charge. But these are low intensity and usually microsecond phenomena.

But I know of no way to run a DC, CW high power discharge for months from an insulator.

Please explain.

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originalJohnPosted on 28/07/2015 at 17:00

Well, Harvey, you ignore the main issue of my post, the temperature of the bright patches, and choose to focus on the discharge, with a note of sarcasm, and the typical implication that if you cannot envisage it it must be impossible.

Nevertheless I will outline the charge/discharge mechanism for you and show you that there are some things you perhaps simply cannot envisage. I will first remind you that whereas you ask the question HOW does the charge/discharge occur, this is in fact an experimental mission and both the orbiter and lander are capable of answering the far more significant question DOES a charge/discharge occur.

So. the comet nucleus is a non conducting body because unlike in the metallic bond, which has some mobile electrons, all of its structural electrons are bound. As the orbit is a repeating cycle we can start at any point. I choose to start as the nucleus approaches aphelion having attained a state of neutrality.
It is moving at its slowest through a region of the solar electric field near or just beyond the orbit of Jupiter.

It is immersed in an environment of negative charge and by a process of electrostatic induction a positive charge is established at the surface of the nucleus. This occurs by polarization of the sub atomic charges, the atoms and the molecules so that the positive poles are aligned facing the nucleus surface. A potential difference is therefore set up between the surface and the surrounding negative charge causing electrons to migrate to the nucleus surface. The surface acquires a negative charge and this migration continues until a state of charge equality with the surroundings is reached. The electrostatic force maintains the sub structural polarity of the nucleus.
This is a transitory state because the nucleus is starting to move towards the Sun and continuously encountering regions of more positive potential. The surface electrons and other negative ions therefore begin to discharge to the surrounding virtual anode of the plasma. Neutrality cannot however be achieved as the accelerating nucleus constantly encounters new regions of higher positive potential in the solar electric field.
As the nucleus surface electrons are surplus and free they generate conducting current paths and the discharge sites are able to be replenished by gathering electrons from all over the surface.

And so on, with increasing positive potential in the field and increasing discharge intensity as the acceleration of the nucleus continues.

The next key stage is as the nucleus approaches perihelion. It is entering the most strongly positive region of the solar electric field and there are several possibilities. Let us assume its surface charge of electrons has been exhausted. It briefly once more attains a state of neutrality and the polarization of its structure is lost.

It is surrounded by positive charge which electrostatically induces a charge at the nucleus surface by structural polarization but now of the opposite polarity, with negative charges pointing to the nucleus surface. The potential established causes surrounding positive ions to be attracted to the nucleus surface and it tends towards charge equalisation.
However, the nucleus is now starting to move away from the Sun, no longer accelerating but continuously encountering new regions of more negative potential so it continues to discharge, now positive ions held as a positive charge on the surface by electrostatic force or positive ions released in surface reactions. This proceeds at an ever decreasing pace towards aphelion where the cycle begins again.

This is an idealised explanation. There are many variations in coordination possible and other parallel processes going on Also I emphasise that electrostatic induction is standard electrical theory, and the rest is standard electrodynamics.

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HarveyPosted on 29/07/2015 at 19:50

It isn’t an explanation at all; its complete nonsense.

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HarveyPosted on 05/08/2015 at 15:02

So, why is it ‘nonsense.’

That falls in two categories.

Firstly it is simply *asserted*, with no explanation or justification, that:
“It is moving at its slowest through a region of the solar electric field near or just beyond the orbit of Jupiter. It is immersed in an environment of negative charge………”
(BTW Confused; charge & field are related by Gauss’ law & not interchangeable terms.)
“This is a transitory state because the nucleus is starting to move towards the Sun and continuously encountering regions of more positive potential. ……….”
There is no evidence for this and, effects mentioned below of small magnitude aside, not true.
Regions of space are not ‘negatively charged’; one a scale of a few times the Debye length, it is neutral. This is first year physics & in every plasma physics textbook there is. The Debye length is order tens of metres in interplanetary space. It’s pretty intuitively obvious; any charged region attracts the opposite charge & self neutralises, vey crudely.
There *are* two mechanisms giving rise to *weak* fields. Firstly (solar wind V)(vector cross product)(interplanetary B, magnetic field.) A small field pointing at right angles to V & B. Secondly, an infinitesimal field due to the fact that the sun *does* have, it is thought, a small positive charge. This originates since more electrons reach escape velocity than protons due to their lower mass; the resulting field restores equilibrium. From memory the charge is <100coulombs & the voltage low kV; the field even at 1AU is infinitesimal & I don’t believe has ever been observed.
So the basic tenet is simply wrong; these ‘charged region’ & large electric fields don’t exist.
Secondly, a totally confused view of electromagnetic induction and its implications.
A little consistency would be nice of course; we are told, correctly that: “So. the comet nucleus is a non conducting body because unlike in the metallic bond, which has some mobile electrons, all of its structural electrons are bound. “
But a few lines later:
“ A potential difference is therefore set up between the surface and the surrounding negative charge causing electrons to migrate to the nucleus surface. The surface acquires a negative charge and this migration continues……….”
THEY CAN’T MIGRATE; as you told us, the electrons are bound; they can’t migrate *to* the surface, & any that arrive there from an external source can’t move *on* the surface; ITS AN INSULATOR; you have confused what happens in conducting bodies with what happens to an insulator.
For an insulator NO charge migration occurs; the body becomes *polarised*, with the + & – charges slightly displaced from equilibrium but still bound in place.

There seems to be complete confusion about whether we are moving from regions of differing field (true but tiny) or regions of differing charge.
If differing field, the comets polarization simply changes to respond to that; no charge carriers are available to run some mysterious discharge.

Nothing in the law of electromagnetic induction helps you run some mysterious discharge.
For an insulator, *NO CARRIERS CAN MOVE*, that’s what an insulator is.
For anything, somehow you have to satisfy charge conservation; electrons can’t be produced out of nowhere; there has to be a source & a sink.

Finally, numerically, the whole thing is encapsulated in one simple sum.
The comet has a capacitance of less than one microfarad; first year physics.
Put a GIGAVOLT on it (I think we’d have noticed) & you get 1000 coulombs; which will run a tiny 1A discharge for 1000 seconds, 20 minutes.

On one more thing we agree:
“Also I emphasise that electrostatic induction is standard electrical theory, and the rest is standard electrodynamics.”
Trouble is, you have to understand it to use it.

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ianw16Posted on 29/07/2015 at 21:07

All this assumes a distant dependent electric field around the Sun. And the evidence for this is…………….?

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originalJohnPosted on 05/08/2015 at 16:17

The evidence is w16 that the solar wind is a flow of charged particles. What moves charged particles ?
An electric field. Hence the acknowledged heliospheric current sheet.

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HarveyPosted on 10/08/2015 at 12:20

Electric field *accelerate* charged particles; and they accelerate electrons and protons *in opposite directions*, which is a bit of a problem for you.
It’s perfectly possibly to have a high velocity particle beam in a field free region, we do it all the time in accelerators etc.
They can also be accelerate simply by thermal energy, a with that fraction above escape velocity escaping, which works for both.

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HarveyPosted on 10/08/2015 at 13:18

Sorry, correction. It can’t be ‘field free’ if it’s an un-neutralised beam, there will be at least a radial field due to the operation of Gauss’ law., Div E=rho/eps in differential form. The beam blows up under its own space charge.
What I meant was free of the field that accelerated the particles to high energy. That is routinely true.

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originalJohnPosted on 10/08/2015 at 14:48

Jumbled ramblings Harvey, illustrating your lack of grasp of the interplanetary medium. And convenient figures plucked from the air to create a pseudo mathematical authority.
I advise you to stop using argument based on Debye length because you still do not understand what it means. The electrostatic interaction between positive and negative charge occurs only within the Debye length. Beyond the Debye length natural screening occurs and the ions behave as separated positive and negative charge. The neutrality is quasi, meaning not real. There are equal numbers of positive and negative ions but they do not interact. They remain as separate ion streams. That is what a plasma is. And that is what the solar wind is. So your concept of neutrality in space is wrong. Until you get that right much of reality will be beyond your imagination.

It is recognised that a current sheet exists in the heliosphere. It is also recognised that the interstellar medium is electron rich. The proton current flows from the Sun to the virtual cathode at the edge of the heliosphere. On that basis alone the Sun is an anode.

As for insulators the structural electrons are bound. The charge electrons at the surface are free, surplus to structural requirements. They are nothing to do with the non conductive properties of the insulator. Under discharge conditions they can move freely on the surface. This phenomenon is well documented on the surface of the Earth with lightning discharge.

Indeed you have to understand it to use it.

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sjastroPosted on 11/08/2015 at 23:09

@originaljohn,

Please explain how the solar wind which is composed of both positively and negatively charged particles is being driven IN THE SAME DIRECTION by this “electric field”.

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ianw16Posted on 29/07/2015 at 20:56

You seem to be forgetting that at this, and other comets, the temperature of the sublimated water vapour has been calculated.
For close nucleus observations at this comet, the temperatures were not only below 0 C, but considerably below it. This was in the MIRO data from months ago.
You also seem to forget that water vapour heated to the levels you suggest, would be escaping at a considerably greater velocity than that which is observed. The velocity measured is well in line with models of sublimated H2O escaping into a vacuum. Heat it up, and the velocity will increase noticeably.
Then there was the MIRO mm and sub-mm measurements of the subsurface temperatures. Again, a long way below 0 C, and no anomalous 400 C spikes seen.

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originalJohnPosted on 30/07/2015 at 20:36

How close to the nucleus w16. Any temperature for the discernible jets, say at zero to 4 kilometres.

The water vapour in your gas boiler flue is heated to well above 400 deg C. What do you think its velocity is. Actually a lot less than the measured velocity of the jets.

At how many points on the surface were the sub mm measurements made and in what regions in relation to activity. And that was below the surface, not at or above the surface where the heat would be from a combustion plasma/discharge reaction. The heat below the surface would fall off rapidly.

There were some VIRTIS measurements of the surface last year and from a few hundred kilometres. It was observed by THOMAS on here that there were numerous hot spots (white) and a continuous hot band along the valley between the two lobes, where all the jet activity was occurring at that time. These received no comment from the investigators. The maximum temperature inferred was 230 deg K. This however was the saturation level of the instrument. So all temperatures above 230 deg K were recorded as 230 deg K. So the temperature of the hot spots was unknown.

In reality, the maximum temperature measured WAS 230 K. Temperatures of this magnitude were obtained at various locations on the nucleus surface experiencing maximum solar insolation with small incidence angles.

You write: “This however was the saturation level of the instrument. So all temperatures above 230 deg K were recorded as 230 deg K. So the temperature of the hot spots was unknown.”

WRONG! WRONG! WRONG! And WRONG! Here are the FACTS …

Your statement indicates to me that you have made no effort to investigate the scientific capabilities and dynamic range of the Visible and Infrared Thermal Imaging Spectrometer. It is such an exquisitely engineered piece of kit that it was selected to fly on three different missions – the ESA’s Venus Express and Rosetta, plus NASA’s Dawn. As an aside, the instrument actually flown on Venus Express was the Rosetta mission spare! Cool? No?

Design specifications for VIRTIS are available online (Bonsignori et al (1997), Coradini et al (1998) and others). From the design specifications there are a couple of features that are worth highlighting here. The VIRTIS optical subsystems (-M and -H) are housed inside a cold box that is passively cooled to ~160 K. The IR detectors require additional cooling to ~85 K. This task is accomplished using closed-cycle miniaturized cryo-coolers. To avoid large measurement errors caused by thermal “noise” from the walls of the instrument, the lowest temperature that can be measured is ~170 K.

So we’ve established the minimum temperature that VIRTIS can measure. What is the maximum? Following the Venera, Pioneer Venus, and Vega missions, the Venus International Reference Atmosphere was established. VIRA sets the average surface temperature as 735.3 K at 92.1 bar. The following table gives the minimum and maximum temperatures reported for the five solar system objects investigated by VIRTIS instruments.

Note 1 – The temperature values for Venus were obtained on the night side of the southern hemisphere.
Note 2 – Mineralogical calibrations for VIRTIS on Venus Express were conducted using a reference temperature of 770 K.

Obviously VIRTIS is capable of measuring temperatures in excess of 700 K. Thus, the values reported by the VIRTIS science team for 67P are correct! Your claim that the instrument was saturated is wrong. I hope this is the last word on this topic.

They actually saw parts of the surface reach a whopping 230…….Kelvin.
And………….” so far there is no evidence of thermal anomalies, i.e. places of the surface that are intrinsically warmer or cooler than surrounding terrains observed at the same local solar time and under similar solar illumination.”
This was all the way from 3.59 -2.74 AU.
.

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loganPosted on 23/07/2015 at 22:05

In the hypothetical case of liquids, there is no reason for them to drain all the way to the gravitational center(s). Even is all porous. At some point adsorption an other VDW forces take precedence over gravity.

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HarveyPosted on 24/07/2015 at 16:58

Logan, agreed. The Maragoni effect I’ve been going on about is caused by surface tension varying with temperature, and surface tension originates in van der Waals forces.
This is again an example of earth bound common sense and intuition being dangerous on 67P. Liquids will not behave in the way we ‘know they do’.

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MarcoPosted on 24/07/2015 at 21:53

Hi Logan, someone has done the calculations in this regard (haven’t been shown the detail as it is proprietary :-(. )
It appears that gravity is cancelled out by the other various forces in microgravity. What is left is that the flow of internal liquid is governed almost entirely by centrifugal forces. Thus if there is liquid inside the comet, it will migrate outwards from the centre of gravity towards the crust. To be consistent with the conclusions from stretch theory, a kind of mud would be sitting under a hardened hydrocarbon crust of about 50 metres, under the whole surface of the comet.

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A. CooperPosted on 27/07/2015 at 09:05

Marco

I think your pooling liquids idea has a lot going for it on Imhotep. I’ll make some observations and suggestions as to mechanisms involved, outlined below.

I would note, first of all, that viscous flow and slumping of slurry is already evident on Seth (at its southern extension bordering Hapi) as is scouring and ‘fanning out’ of conduits a little inwards from the slumping, so the following ideas for Imhotep aren’t entirely speculative. On Seth, these phenomena are visible in the slumping and hardening of the two 40-metre-high slurry piles that were emerging from under the ‘gull wings’ on the Seth/Hapi border. They hardened in mid-slump, it appears, and might contain as much as 50,000 cubic metres of slurry.

Regarding Imhotep, the lowest point marked by the ‘x’ in the scientific paper is probably the source point of the slurry that was coming from under the stratum layer that contains the flat area ‘D’. So, like at Seth, slurry was running along the fracture plane between strata. It came from under D and out where the roundish features are (but the roundish features weren’t yet formed and appeared soon afterwards).

The source area is fan-shaped with what appears to be heavy scouring on the north side of the fan (shadowed in this blog post’s hi res photo). There’s some scouring to the northeast between the shadow and the giant boulder. The curve of the fan runs from the shadow, through the tip of the boulder and past the top of the ‘E’ to the two large, southernmost roundish features. The southern side of the fan would be the curve of the deeper area perimeter round to the two roundish features. This fan shape and scouring resembles the character of a spring or a water mains leak or aftermath of a severe flooding event. The flow is from the east, from under the flat area stratum, out towards the giant boulder. There are three slurry pool remnants in the low areas next to roundish features. Much of this outflow and scouring happened under the barely risen Imhotep slab so the slurry wouldn’t necessarily have been subject to the full vacuum and yet would’ve been explosive on emerging from the source due to some pressure drop.

It has to be borne in mind that any slurry running along the fracture plane wasn’t only under pressure. In stretch theory it was experiencing negative g and being pushed out of the fracture plane via ‘centrifugal’ force. Once it emerged on the surface and the Imhotep slab had left, it was presumably kept from escaping by its sticky, cohesive nature that would overcome the circa 0.1mm/sec^2 negative g acceleration. The negative g however means much more scope for slurry filling up a large portion of the fan area.

Conversely, only half an hour or so after the comet started stretching, the g force on Imhotep would turn positive again due to AM conservation and rotation period slowdown. This might even mean the pool partially draining back down under the stratum it had come from.

I believe the so-called roundish features are just plain old geysers, although repeated bubbling might form a conduit of a sort. The gas source would be from the pool in general and not some specific fracture under the geyser so the term is used loosely. The circles we see would therefore be the result of the last few bubbles of gas pushing their way through the edges of a pool of rapidly hardening slurry. The slurry would presumably turn viscous and harden very quickly after emerging from the comet interior. The roundish features are arranged around the edges of the pools. I would suggest that their rim heights betray the former slurry surface level, or at least the surface level of the pool edge where the last bubbles were pushing through a hardening slurry but the deeper, more fluid centre of the pool was draining back down into the fracture plane a little. So today we see three residual pools (plus some very small ones) with apparently marooned geysers around their edges. The notably wide band of geysers on the east side of the two adjoining pools would be consistent with successive lines of geysers turning solid as the pool edge receded down the gentle slope.

The slurry would be expected to harden quickly. However, in the initial stages of the missing slab scenario, the pressure would remain high in the tiny crevice between comet and slab, while slurry was being injected between them. This might be enough to keep gases from evaporating and the slurry very fluid.

This could allow enough time for thousands of cubic metres of slurry to escape and swill around in the fan area within the crevice. As soon as the slab lifted off, a skin would form (presumably), the slurry would become viscous and it would eventually harden. In the meantime, viscous flows and slumping might have occurred as the gases wouldn’t escape instantaneously. This would have been when the pools receded, leaving their marooned geysers round their edges.

That fan area is explained via liquids being injected under the Imhotep slab from one stratum further down, pooling in the fan area and leaving geyser-like features at the receding pool edges.

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RamcometPosted on 28/07/2015 at 06:25

A. Cooper, I have been visualizing this for some time from my crazy lifelong arts and crafts experiences. Thickly skinned cylinders like around old paint, resin or tar buckets, left over after geyser activity. That’s why the cylinder “cups” still protrude above the dust or other plains.
And other features looking just like peeled up fractured resin layers on the floor of a surfboard shop. There is even one recent image showing half of a geyser hole hinged up 90 degrees! I will go find it and report back.

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A. CooperPosted on 30/07/2015 at 00:06

Ramcomet

I still remember your muffin mix recipe for the expanding neck. It helped me see other analogies like spray foam insulation that expands due to carbon dioxide fluffing up a matrix of organic chain polymers. I should think a can of that would go quite a long way on 67P being sprayed into a vacuum. The unstretched core was possibly like a can of spray foam thats frozen more than pressurised. Expansion is an interesting idea and Anuket seems very much to exhibit that expanded, reworked/homogenised character.

It’s interesting you mention hands-on arts and crafts experience. I have a couple of arts and craft friends who can flip complex shapes around in 3D in their mind’s eye as a matter of course. And they juggle mirror images as well as more complex chirality, topological concepts, transformations etc. without knowing what they are. They are nonplussed as to why I’ve had to write a 100,000 word blog with hundreds of annotated photos to explain what they can see by glancing at half a dozen 67P pics from August 2014. I think we need a few more artists to join in the discussion.

I agree very much with your paint skin analogy. The circular ‘geyser’ rims may well have set due to repeated concentric waves hardening a static ring of slurry that was setting at a certain radius from the bubbling. That is, static but for being repeatedly pushed up in a raised ring, which itself would increase surface area-to-volume ratio, enhance volatile evaporation and accelerate hardening. These rings would be deposited on the lake shore as the lake receded and the trapped slurry within would continue to lose its volatiles, slumping into a concave formation within.

Did you ever PM me on the blog? I couldn’t see anything.

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A.CooperPosted on 30/07/2015 at 22:30

I wasn’t going to labour the point about 67P having all but one of the ingredients to make spray foam insulation because I just saw it as an amusing coincidence. But as if on cue, the Philae science papers, out today, have found methyl isocyanate. Isocyanates were that missing ingredient although apparently methyl isocyanate is used for rubber production, not expanded polystyrene. I very much doubt the ingredients were all sitting there in the correct proportions anyway but maybe it’s food for thought for a contribution to the apparent neck expansion.

BTW, Ramcomet, I didn’t quite get the varnish layers in the surfboard shop comment. I get the analogy so I can visualise what you mean. I’m just wondering where on 67P I should be looking for it.

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A.CooperPosted on 30/07/2015 at 22:41

Ramcomet

…or maybe you meant the successive strata layers that have peeled away? That’s especially evident on Imhotep. I mentioned the fan-shape being the “second stratum down” for the sake of not confusing matters. But really there seem to be four main (50-metre-plus) strata missing if you trace the strata terraces back to Aten and Apis.

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HarveyPosted on 28/07/2015 at 09:31

‘Slumping’ requires gravity; ‘slurry’ implies high viscosity, opposing the slump.
Geysers are buoyancy driven, by gravity.
‘Fluid draining back’ – gravity, opposed by viscosity and potentially surface tension effects.
‘Slurry *level*; our concept of a flat fluid ‘level’ is gravity driven.
Gravity is some 10,000 times weaker on 67P.
I have no confidence at all such mechanisms work there.

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A.CooperPosted on 30/07/2015 at 02:19

Harvey

Captcha hurled my reply to the bottom of the thread…..

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MarcoPosted on 28/07/2015 at 11:31

A.Cooper

I do like that better than my not so specific mechanism.

-> Imhotep slab flies off exposing a liquid hydrocarbon/mud layer below. Liquid layer finds equilibrium the best it could, covering the lower areas which hardened flat, and filling in lakes which are the roundish features with separate flat floors.
Surface fluid hardens from the exposed surface down, evaporating volatile species in a fractionation process which concentrates PAH’s.
The current areas which show most jets should be the areas with the thinnest crust, which should be predominantly near the fractures around Imhotep.

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MarcoPosted on 29/07/2015 at 21:46

Harvey,
There is no need for us to be in the dark when it comes to liquids as envisaged by me and A.Cooper on 67P. We have a perfectly functioning space station for experiments with and without liquids of all sorts.
Hot chocolate should have the properties required, because it hardens from the outside in, with a temperature dependent viscosity, which mimics the exposure dependent viscosity of the liquids under the surface of 67P.
Surely, in the meantime, a thought experiment along those lines would indicate that a complete lack of liquids is ruled out, specifically due to microgravity allowing non liquid things to be untethered and escaping at the slightest provocation.

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HarveyPosted on 30/07/2015 at 17:22

The properties in so called zero g are perfectly well known and there are plenty of videos.

Liquids behave utterly differently; they form free floating wobbly blobs, which can have internal bubbles which stay there.

It’s a problem fuel tanks on spacecraft; if you have fluid free in a larger space, it’s hard to know where it will actually be. It’s position becomes determined by surface tension effects, Matangoni flow etc. You either avoid having a free surface by having a flexible diaphragm with gas behind it, or you impart a small acceleration in a known direction (eg with a small solid fuel motor) to get the fluid in the right place.

On 67P, it’s a bit different, because although the gravitational field is small and variable in strength and direction, it’s not completely negligible. The results will be quite sensitive to size scale, timescale, viscosity, surface tension, surface tension change with temperature……unless you actually know these, an experiment won’t tell you a lot.

So you need detailed consideration with quite a bit of care. It’s an intermediate case, more towards the space station end than the earth end, but not actually either. I don’t really think hot chocolate will tell you a lot, sadly 🙂

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MarcoPosted on 31/07/2015 at 10:56

Harvey,
Hot chocolate experiments may or may not give useful answers to 67P but it would make a damn tasty treat after a hard day’s experimenting 🙂
I think you are still missing the point that 67P has done the experiment for us – We are just interpreting it. There are three states available (Actually four – with plasma) to interpret the evidence. Space station experiments with and without liquids, but rough approximations of what sort of material is available, would certainly show that a lack of liquids makes flat areas virtually impossible to be an expectation of the resultant morphology.
It is not because of plausible positive results with liquids, but the implausibility of positive results (flat areas) without liquids.

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davePosted on 29/07/2015 at 15:03

Re A Cooper,

Enjoyed your blog on slumping slurry, even it it does not turn out to be viable, its good to see some one look at alternatives than just plain sublimation. It would be nice to see some more comment from the ESA team ref the deep pits. Your article at least gets us thinking along different lines.

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A. CooperPosted on 30/07/2015 at 01:55

Harvey

Yes, slumping requires gravity. Slurry implies high viscosity but only in relation to the conditions in which it’s being analysed. Anything that’s viscous on Earth would probably act like solid rock on 67P. Conversely, anything that’s viscous on 67P would slump to a flat pancake on Earth. But we’re talking about something that’s viscous on 67P, not something that would be classified as viscous on Earth according to a table of Earth-based slump experiments. So it’s behaving like something viscous would behave on Earth and that’s because it’s comparatively fluid but under the influence of 1/10,000th the g acceleration.

Geysers are buoyancy driven on Earth. Geysers are also characterised by gas bubbling through slurry. I’m describing a scenario on 67P whereby gas bubbles through slurry by whatever means, whether buoyancy-driven or by brute force of gas pressure.

I had said I was assuming a sustained and substantial gas pressure emerging from the source. If it was bringing slurry up with it then gases would be, by definition, arriving at the fracture plane outlet and finding themselves at the bottom of a pool of slurry. Yes, without substantial gravity-driven buoyancy they would build up and up. But if the flow pressure continued relentlessly, then eventually the gas bubble would be doming so high, pushing up the lake of slurry, that it would have to escape somehow. If, due to viscosity, the lake was reluctant to slide down the sides of the giant gas bubble and round to its underside, allowing it to escape, (gravity-driven buoyancy), then the bubble would simply find the path of lowest resistance. That would have to be out through the sides of the domed lake i.e. its ‘shoreline’ touching the comet surface around the bottom of the dome.

That utterly bizarre scenario probably never came to pass but it would if a) the gas pressure was relentless and b) the slurry resolutely refused to play ball in the gravity-driven buoyancy game. One other non-buoyancy scenario would, I suppose be admissible. That would be where the gas did force the slurry lake upwards but just to one side, escaping in the process. If the lake just remained in mid-air, like an angled, solid slab and didn’t fall back down because the gravity is so weak, that would allow the gas to escape without allowing the gravity-driven aspect of buoyancy to prevail. But of course, the slurry slab would have to harden very quickly and to a tensile strength that supported it at its base. In reality, it would almost certainly drop or snap- or slump, thereby satisfying the gravity-driven aspect of the buoyancy but in a very belated manner. All highly unlikely anyway but I’m just trying to accommodate your scepticism over whether gravity driven buoyancy would operate. But if the gas pressure was relentless then something had to give. I think something along the lines of the doming and and escape at the shoreline is possible but with a much-reduced dome. That would satisfy the fact that the geysers line the shoreline of the lakes.

“”Fluid draining back”- gravity opposed by viscosity and potentially surface tension effects.” I agree but that’s why I said “might even” and “partially” draining. However your mention of viscosity and surface tension effects may answer the question as to how the pools receded. If these qualities are lot more influential than the gravity (which I agree they are hence saying the slurry stuck to the comet despite negative g) then it means that when the Imhotep slab departed, it took half the slurry lake with it, stuck to its underside.

As for “slurry level”, I was saying just that, not “level slurry”. I was using the word, ‘level’ in the sense of it being a particular height datum point in the ‘gravitational height’ topography scale. True, I used it thinking of the level of the lake shoreline being pretty well the same gravitational height all the way round as it receded. That’s because the notion of whether the lake surface was a gravitationally ‘level surface’ (like a lake on Earth) was immaterial to the point I was making that the shoreline was receding as it dropped in terms of gravitational height. I was emphasising the reason for marooned geysers being the receding lake shoreline. I wasn’t contemplating whether that shoreline was a level surface at all. I’m well aware that it didn’t have to be. It could even be up and down, all over the place but with the average height nevertheless receding. So, yes, the shoreline could go up and down as it battled all manner of surface tension and viscosity issues scuppering its ‘attempts’ at staying level in the gravitationally level sense. It’s quite obvious that the lake surfaces couldn’t be exactly ‘level slurry’ surfaces anyway because they hardened with ridges in place.

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HarveyPosted on 31/07/2015 at 10:13

To get earth like gravity driven phenomena, you need to maintain the ratio of viscous to gravitationally driven forces. That means viscosity some 10,000 times lower.
I don’t think there are any candidate materials with a viscosity anywhere near that low, let alone ones compatible with the environment and temperature; viscosity tends to increase rapidly with reducing temperature. You can get water like viscosity at low temperature, Liquid nitrogen at 77K for example is about half water at 300K. But at 200 odd K most organics will be pretty viscous.

Many of these effects are non linear and require critical parameters to be exceeded. You can’t just assume whatever happens at 1g happens slower; it may not happen at all. Convection, turbulence a etc require critical Rayleigh, Reynolds numbers to be exceeded. Some of these processes will behave like that.

You can’t ignore surface tension; it becomes very important in low g and can dominate everything else.

Geysers incidentally also depend on a heat source ‘from below’, and heavily on the increase in boiling point with hydrostatic pressure, a very, very small effect on 67P. (Not long ago returned from a holiday in Iceland, where we visited Geysir, as it happens. The original Geysir died long ago, there is a small, not that spectacular one. New Zealand has fantastic example on N Island.)

The putative liquid seems to have a rather restrictive range of special properties, which stretch credulity for me. I’m not at all sure there are actually credible candidates.

What exactly liquids, slurries *would* do, if they exist, on 67P I would not care to predict without a great deal of thought and analysis. But I doubt they would behave *anything* like they would on earth, and those concepts embodied in words like slump etc are likely to mislead.

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A. CooperPosted on 04/08/2015 at 02:45

Harvey

“That means viscosity some 10,000 times lower”.

Imagine a blob, let’s say a cone of this supposed slurry that’s the size of a 7 story office block. It’s sitting on 67P and arrived there by whatever means. Granted, cohesive forces would hold sway towards the top of the cone. But the pressure on the bottom ‘floor’ of this blob is far greater than at the top due to the greater mass (above it) x acceleration. This in turn causes an outward pressure at the base.

I contend that the top 6 floors can act as a bulk liquid, as you imply, thereby satisfying the reluctance of the liquid to flow due to the ratio of viscous-to-gravitational forces not being surpassed. But this many floors (or however many necessary floors) will create enough gravitational force at or near the base of the cone to surpass the ratio and initiate flow within that bottom layer. The only way for it to flow is outwards, radially. This means that the top six floors of the cone will drop to take the place of the bottom floor. Therefore, we have slumping.

It means that the viscosity would not need to be 10,000 times less. That’s because the top six floors remained in bulk status and thereby ‘donated’ their gravitational force to the bottom floor. And when I say “gravitational force at or near the base” I don’t mean gravitational acceleration which is constant in any given place on the comet and very small. I mean the force as built up by the mass accumulated above the bottom ‘floor’ times that constant acceleration.

This isn’t a stunning new insight, as I’m sure you know. Civil engineers conduct slump tests on concrete on a regular basis before giving the OK for the pour. They have to keep adding concrete to the pile until they can’t get it to go any higher and then measure the depth. When they reach that steady state, they have, by definition, a cone of concrete that is acting in bulk status, whereby gravity is unable to overcome the viscous force. If they then add so much as a spoonful, they see slumping. But the slumping is a spreading out from the bottom while the bulk status cone sinks to take its place. If you keep adding concrete to the top, the cone eventually ends up on the ‘bottom floor’ and is then indeed subjected to the domain in which the gravitational force overcomes the viscous force. It gets forced out radially and so completes the slumping cycle.

It still means this slurry on 67P has to be much less viscous than a liquid with the same apparent viscosity would be on Earth but not 10,000 times less.

You mention the compatible environment and temperatures. All these major slurry scenarios (at least four dotted around the comet) are evident either on the shear line or under erstwhile slabs. They are one-off scenarios that couldn’t hope to be instigated via solar radiation energy input. They could only be instigated via a very short, sharp energy input. It has to be short and sharp because power, in the technical sense of energy/time is crucial to getting a sudden, substantial rise in temperature before it conducts or convects away. Seeing as these slurry signatures are most noticeable at the shear line (and, dare I say it, even the slurry matches from head to body) it’s only reasonable to work along the hypothesis that it was the stretching prior to shearing that generated the heat to sublimate so much gas that pressures built up, dykes were scoured, and liquid states were maintained if only for a very short period. Scouring dykes with liquids and/or gases would produce slurry that could go only one way- out to the shear line.

And at Seth, they produced not one but two cones the size of a seven-storey office block. Did you take a look? If not I would suggest you take a look at part 7 of the stretch blog. If you still need more convincing you could look at the Hathor dykes in part 8 and Bastet dykes and slurry in part 21, or the slurry signatures (yellow match) in part 24, or the scouring in part 5 which also shows matching dykes betraying how they imprinted themselves on either side of a fracture plane before it sheared apart, or scroll down to see the ‘rope line’ of slurry that pushed up the frill that’s so evident on the head rim above.

So, no it’s not misleading to talk of slump. It’s at the very least a reasonable working hypothesis based on the visible evidence and the fact that the evidence is found only where you’d expect it to be- all round the shear line and at the two extremities. That’s more than can be said for the multitudinous references to ‘erosion’ without citing a single rock or pebble that has been seen to move.

If you want to slay the slurry theory, you may get some mileage in looking at the energies required via stretch for such a temperature rise. I can’t get them to add up but that’s based on the supposed crustal tensile strength, not the unknown core strength. I’m only doing that because there is such an abundance of evidence for slurry all around the comet just where you’d expect for stretch to have caused it. You’d also have to explain what these strange dykes and ‘slurry’ piles actually were if not dykes and slurry piles. Whether it’s slurry or not it has no bearing on the soundness or otherwise of stretch theory.

Regarding Reynolds numbers, that’s addressed in the cone scenario. Regarding Rayleigh numbers, I said in the last comment that we are working on the assumption of sustained gas/slurry pressures and therefore brute force. Perhaps, I should’ve mentioned the power-intense stretch energy input in that comment to explain the abundance of gases/slurry. I also said that I was citing geysers in the sense that they were a phenomenon whereby gas gets forced through slurry by whatever means and there ends the analogy. Heat sources aren’t needed for bubbling here except in the indirect sense that heat energy was needed (via stretch) to generate the gases that caused the sustained pressure.

Regarding surface tension, I absolutely agree that it would reign supreme for shallow ponds and coatings, but for the bulk status cone scenario it’s negligible. However, I suspect you were implying cohesive forces when saying that, so yes, those would impact on viscosity.

Regarding hydrostatic pressure being a very small effect (though not needed with brute force gases), it occurred to me that a Lake Nyos-type catastrophic turnover might happen. Nyos was probably caused by a landslide but could theoretically have been caused by an earthquake. If these gases on 67P were being ejected due to spin-up and foreshadowing imminent shear, I should think the duck was tremoring from head to flipper by this point. Oh, except it wasn’t a duck at that point 🙂

Here’s a quote from the Lake Nyos wiki page:

“The event resulted in the rapid mixing of the supersaturated deep water with the upper layers of the lake, where the reduced pressure allowed the stored CO2 to effervesce out of solution.”

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HarveyPosted on 05/08/2015 at 09:18

Your last sentence encapsulates the problem of much of the argument.
‘The reduced pressure……..’
On Earth, you get one bar for ten metres of water.
On 67P, you get one bar from 10,000 times that, 100km, far bigger than the comet.
(No, I’m not suggesting there is liquid water!)
Hydrostatic pressure effects and gravitational forces reduce by 10,000 times. So significant supersaturation by a gas is not going to occur, it’s very like the geyser, no significant superheat. Also when the gas does form a bubble, the bubble will not rise rapidly to drive the turn over.

Viscosity, surface tension etc all remain more or less the same, and there are no materials with those effects 10,000 times lower, or anywhere near that number, especially cold. It’s not clear whether it would ‘slump’ at all, or ‘slump’ in slow motion. If it’s a ‘critical parameter’ type phenomenon (I don’t know, but it seems that way from casual observation) it’s probably not going to occur; if the latter, ‘slumping’ maybe stands a chance.

Liquids, slurries, are credible if difficult under 67P conditions.; they would probably be transient if they ever exist.

But it remains my view that descriptions in terms of commonly observed 1G phenomena are very risky and likely to mislead. How they would behave would need serious effort – and that is problematic without detailed properties, you’d have to model a range.

A problem will be getting the right people with the right knowledge and skills involved;, they won’t be in the ‘comet community’. The liquids on moons are in far higher G, the only people dealing with liquids in low G are the spacecraft engineers really, and there it’s pretty much a done deal.

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MarcoPosted on 07/08/2015 at 08:08

A.Cooper
The corollaries to stretch theory both completely constrain explanations regarding the source of energy for the temperatures required for liquids, and explain why liquid flows are initially explosive but ephemeral in nature as surface flows.
There are sequential steps to this chain of evidence and constraints. Firstly, the evidence of matches mean that erosion from the outgassing is not happening on or near the surface. Thus the outgassing can only be coming in from deep under the surface 50m or so. The energy can only come from conduction through the crust. There is no other way enough energy can get down deep enough in the quantities required for the observed outgassing. This can be compatible with physics and plausible materials, but requires us to unlearn what we think we know about comets now (As opposed to what they were at the birth of the solar system)
The corollary to outgassing from below is that there is pressure built up under the crust that is only gradually being released by the jets. This pressure may be 10 millibar or 100 millibar. Way less than atmospheric pressure, but enough to keep water liquid above 0 degrees centigrade. Which brings me to the temperature. The temperature will be high enough to keep the lighter hydrocarbons (say Methane, Ethane etc.) constantly liquid. The latent heat associated with billions of litres of these liquids will mean a massive store of thermal energy. Through perihelion the comet probably absorbs more heat than it loses through water vapour loss, and at aphelion, the pores close up as the surface cools, and heat loss is very limited.
Internal convection of both gas and liquid acts as an internal thermal energy transport.
Thus when the comet fractures, it is the sudden exposure to vacuum which powers the geysers and ephemeral surface liquid flows, until the fracture is sealed by the ephemeral liquid, which then hardens to resemble the crust.
Therefore NO extra energy is required from the stretch event itself to explain the dykes and energetic outbursts (eg Comet Holmes outburst can be explained by a massive, nearly fatal breach of the comet crust, releasing stored energy all at once)
Deep impact also caused a similar brightening of its comet by a factor of 5 for days after impact.

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A. CooperPosted on 10/08/2015 at 14:07

Marco

Well, that would explain why I can’t get enough energy out of the ‘stretch-before-shearing’ to create the large amounts of slurry (although I reiterate that it’s based on supposed crust tensile strengths and not unknown core strength). Stretch before shearing would be the entire comet deforming along its long axis as opposed to just the neck stretching after the shear. Needless to say, the long axis and the rotation plane are aligned as you’d expect in stretch theory although that alone is not proof of stretch.

Your scenario also allows for the gases and liquids to be readily available fairly nearer to the surface. That’s if I’m right in assuming the convection layer doesn’t go all the way to the centre or is less efficient lower down.

What is certain is that these slurry signatures could only represent a short, sharp transient event where stored energy was suddenly released. You have hit on a good mechanism for that sudden release, in the form of the stored latent heat in the billions of litres of the lighter hydrocarbons. The energy release would be extremely short and sharp if it were due to these liquids being exposed suddenly to the vacuum.

Under this scenario, stretch before shearing would therefore be a corollary to slurry generation and not a cause. The two phenomena would have a common antecedent in the form of the necessary spin-up for both scenarios to occur. The stretch before shearing would slightly precede the catastrophic shearing event, hence its appearing to be the cause. However, the stretching would also make some some energy contribution.

In the light of your comment I’m going to repost a comment below, which was eaten by Captcha last week. I probably didn’t count enough fruit pies.

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A. CooperPosted on 11/08/2015 at 13:46

Marco

Here’s the other comment. I’ve added some bits in square brackets in the light of the discussion moving on in the last week…

The fan-shaped area and the ‘geysers’ was only half the story. I think there’s evidence of slurry going the other way too, spreading over area D in the hi res photo.

It may even explain the most obvious wavy line across Imhotep. If there was enough slurry (and time) to flow out under the slab, across the fracture plane to the west of the slurry source, it would form a shallow lake when the slab departed. This would become the flat area, D, or a part of it. The lake would then undergo viscous flow for a short while before hardening. It would flow back down towards the source, like honey perhaps, becoming very smooth on its top surface. However, the earlier portion of slurry further out across the fracture plane would be less inclined to flow back, being that much more viscous. So the most recent portion of the flow would tear away at some threshold point, most likely in a ragged fan shape and start flowing slowly back down to where it had come from- the other fan with the ‘geysers’. This is indeed apparent on the flat plain, D, in the hi res photo except the ragged fan looks more like a maple leaf…

[In the light of your comment, I now think that it was the initial detachment of the hypothesised Imhotep slab that caused the catastrophic outflow. It was exposure to the vacuum that caused it and yet the suggested slurry would have been constrained to flow west as the slab tipped on its hinge in that obvious gouge where the roundish features are. As mentioned in an earlier comment, the slab lifted very slowly at first due to its wholly tangential velocity component in the initial stages- the slurry would be trapped in the crevice and forced westward towards ‘D’. Also, in the light of what Harvey has said about Earth-like, fluid slurry flows not being achievable I should say the following here. While the hypothesised Imhotep slab was capping off the slurry crevice running beneath it there was more scope for fluid flow. This would especially be the case if your ‘sealed pores’ were well sealed except where the slab detached at its perimeter. Around that perimeter, the slurry would have been exposed to the vacuum, allowing effervescence and literally sucking more slurry out from further down the crevice. After the Imhotep slab departed, the hardening would occur quickly. So the “viscous flow”, mentioned above would be so viscous that it would be akin to a bulk mass flow with some viscous flow at the ends. This would be consistent with my reply to Harvey that said I expected slumping to involve predominantly bulk movements whereby there was no viscous flow within the bulk volume but the mass of the bulk volume timesed by g acceleration might cause the viscous flow threshold to be exceeded at the ‘bottom’ of the pile. As Logan says, “pressure of the ‘particulate column’ [mg’/A] gives a different viscous behaviour from top to bottom”. He also mentions “honey behaviour”. In this case, the ‘bottom’ would be at the lower end of a wide slab of cooling slurry. The slab got shunted, in bulk, some tens of metres downhill to the east causing the flow signatures described below, at either end. It should be emphasised that the flow described would be a one-off sympathetic slumping movement in response to the bulk shunt. The signatures may resemble continuous, fluid flow signatures like water on sand but of course, it couldn’t be an actual river-like flow because the vast slab of cooling slurry, 300 x 400 metres, is smooth and intact, proving that no such fluid flow occurred across or past it]….

Furthermore, the nature of the demarcation line and the contours below it are highly suggestive of a receding flow: a steep, sharp edged cutaway on the SW side of the maple leaf, next to the ‘D’; flow lines back down the slope in the direction of the slurry source; a linear trough at the base of the cutaway and a corresponding linear hump just in front of it, on the ‘downstream’ side; small runnels within the trough; interacting flow lines as they merge and separate at points along the cutaway. It all resembles the erosion of wet sand on the beach by successive waves reaching the same spot each time, pulling sand away from under the cutaway and causing these classic flow-erosion signatures.

[however, this is all achieved here by a one-off pulling by the cooling bulk volume. That pulling action thinned and stretched the slurry surface. This would be the surface next to the tear and what would have been under the supposed slurry skin until just before the tear happened. The thinning and stretching of the underlying slurry, caused by the pull, could explain the apparent fluid flow features. In reality, it would have been a very short-lived viscous flow in sympathy with the eastward-sliding bulk volume. Think of Ramcomet’s old paint pot skin tearing, sliding sideways and the gap between the two skin breaks stretching into flow-like features because it’s half-solidified oil paint underneath the skin. I’ve done exactly that on a paint tray before: breaking the skin on yesterday’s leftovers, sliding it and seeing the flow features between the breaks. Ramcomet’s pots reminded me of this]…

The cutaway line doesn’t appear to be related to any deeper stratum features like some other lines across the flat plain and its cut-away character is wholly different.

The degree to which it has cut away along this line in terms of depth and length of run seems to be mirrored at the other end of this maple leaf shape. The other end would be the wide base of the maple leaf down near the slurry source/roundish features. It could be likened to a wide waterfall. Or potential waterfall, because it froze in mid-flow as it attempted to flow back into the lowest point, the source area. You can see long lines of slumped material like folds in the advancing front of a thick lava flow. Some folds are right on the cusp of making it into the source recess. The ‘lava’ front is diametrically opposite the cutaway and in the direction of flow i.e. where you would expect it to bunch up if becoming more viscous. One paper refers to these very folds as stratification. I don’t think that applies here at all.

Also, at a casual glance from a distance, it seems that the height of the lava front (the folds) is comparable to the depth of the cutaway. It looks like one simple shunt of a highly viscous medium from west to east, which then hardened.

The scientific paper has a map annotated with what are effectively ‘watersheds’ and basins. This maple leaf shape is an extremely subtlety shaped basin. I suspect it would have been a very slight slope all the way from cutaway to source if the lava front hadn’t backed up and hardened with that extra volume in place.

The maple leaf area of the slump mirrors the slurry source fan. Together, they form a pair of butterfly wings that are aligned along the equator, which is the rotation plane. The slurry source is within 200-300 metres of the centre of the notionally flat body lobe underside. So, dead central, on the equatorial rotation plane, the most likely spot for gases to emerge due to comet spin-up.

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MarcoPosted on 12/08/2015 at 12:10

Hi A Cooper

You say”Your scenario also allows for the gases and liquids to be readily available fairly nearer to the surface. That’s if I’m right in assuming the convection layer doesn’t go all the way to the centre or is less efficient lower down.”

The internal convection tries to equalise internal pressures, which carry right through the sealed interior. Near the surface, there is just more opportunity for large pressure gradients because of the proximity of the vacuum of space. The liquids migrate to near the surface due essentially to corriolis effects, and the gases are readily available because transient exposure to space will violently gasify liquids, but also seal up the breach that caused the exposure. This is likely to be the cause of the latest Anuket superjet. Continuing stretch opened up a crack on the neck, which explosively hurled 100’s of tonnes of material in a few short minutes then just as quickly healed itself with the quickly hardening hydrocarbon mud.

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A. CooperPosted on 15/08/2015 at 02:55

Marco

There’s actual evidence of a similar explosive then plugging scenario on the ‘green’ rectangle where the elongated slurry pile is and the frilly head rim sits directly above it. Except in this case it looks as though, being an elongated fissure, a steady-state scenario arose whereby, slurry kept arriving at the fissure which was at the shear line. As soon as it hit the vacuum it gave up any residual gases and added refractory material to the elongated pile, which slowly rose. This pushed up the frill on the newly-cleaved head rim more and more. This pushing up of the frill is a signature of slurry at least trying to seal the gap. It didn’t succeed because the frill was thin and pliant which is why it kept yielding instead of holding firm to contain the slurry and seal the gap.

Meanwhile, more slurry arrived with the expelled gases shooting out over the top of the pile between the pile and the frill. It was probably a very small gap but because the pile had grown so much, it pushed up the head rim frill. The fact that the slurry was constantly arriving and trying to seal the gap means that the pressures upstream were kept high, stopping the slurry from hardening and sealing off the crevice prematurely, further in. This meant that as the slurry kept trying to seal the narrow gap right up at the shear line, all it succeeded in doing was releasing gases that kept the fissure open and depositing refractory material that added to the pile keeping the pressures up.

I think that in the case of your 50-metre conduits that are notionally tubes or dykes, the slurry would have a much better chance of sealing it off, making your ideas quite plausible. But the actual uplifting of the frill on the head rim is the signature that this sealing process is indeed at play, even if on that occasion it didn’t succeed.

The very exact slurry-plugging description above might seem highly speculative and certainly is more so than other stretch theory tenets because it’s going into detailed scenarios that possibly arise from the theory. However we have five glaring pieces of evidence for this scenario: 1) the elongated pile, now sitting marooned on the shear line 2) the frill of the same length and height on the head rim above it 3) what appears to be a fine precipitate stuck to the head rim under the frill and which mirrors the elongated pile below (the match in Part 1) 4) the fact that we’ve come to the conclusion that sudden exposure of liquids to the vacuum is probably the driving force for the sudden gas/slurry outburst scenario and 5) several nearby rope-like elongated piles arranged in straight lines and strangely isolated on a flat fracture plane.

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loganPosted on 09/08/2015 at 15:49

Hi Harvey. Capillarity, confined to points of contact between particulate could give the temp range and this extremely low level of viscosity. Not to forget that pressure of the ‘particulate column’ gives a different viscous behavior from top to bottom.

Defending your posture of transit of material being very dominantly that of solids, but not excluding plausibility that solids [at that extremely low gravity] could show some ‘honey’ behavior.

Of late, being defending Fusion [and capillarity] at points of contact between particles, deep at the particulate column, and with bottom of particulate column. Helped by salts, temperature and pressure.

………….

Not excluding real muds, as the super-structural ‘great-walls’ seems to be formerly made of. Or brines, actually, as a suggestion for ion transit.

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HarveyPosted on 10/08/2015 at 13:07

Logan. Capillary effects are of course another example of a surface tension driven phenomenum. If you look up the equations, they have a 1/g term in them.
So for the same sized tube, and same liquid properties, a liquid climbs 10,000 times higher up a vertical tube than it does on earth! It also goes as 1/r, the capillary radius; so, say, you could have a tube 100 times wider and it would still climb 100 times higher than on earth!
Capillary action, Marangoni flow etc suddenly become massively important, often dominant effects, not the minor things we are used to.https://en.m.wikipedia.org/wiki/Capillary_action

Effects due to hydrostatic pressure are likely to be pretty negligible on 67P, it’s just so small, that goes the other way and reduces in importance.

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MarcoPosted on 03/08/2015 at 13:00

I don’t think we are talking about “corresponding” earth like gravity driven phenomena at all.
Really it is just well known space station experiments extended with thought experiments.
Take the simple act of preparing a meal in space. Many recipes require spreading paste on pita bread. Why not sugar or crackers or powdered spices? Brittle solids don’t have any sticking power under low gravity. They can’t be organised into a meal let alone a flat surface with haphazard natural forces in low gravity.

Another space oddity is squeezing a saturated towel. Rather than dripping, the water kind of slumps, drains and otherwise tries to find equilibrium of sorts with the various forces at work without gravity. It doesn’t need earth like gravity to have these properties. It should not be impossible to imagine a thought experiment that expands a liquid with similar viscosity to water inside the space station to a larger scale experiment of liquid hydrocarbons temporarily on a comet sized body. If we use molten chocolate saturating the towel, that would give us the part of the experiment where the liquid solidifies at the surface. So after it slumps around the outside of the towel, the surface would solidify through cooling on exposed surfaces. Depending on accelerations of movement by the motion of the towel this can simulate tiny gravity. One way or another equilibrium may be reached with a gently curving crust of chocolate. No earth analogies required.

How will they behave? On Small or big batches; Subject to a very light push; Pushed with a slight slope; Rolled on a surface; Strongly pushed; Slowly punching the batch at the center; Freezing; Drying; Making the batch to spin or Impacting it with a projectile.

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loganPosted on 30/07/2015 at 02:49

On awe about the perfect square at fig. 1 of the paper!

Of course, could be just perspective.

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loganPosted on 30/07/2015 at 03:12

“…There are spatial inhomogeneities in the
size distribution of grains in the smooth areas [of Imhotep plains].”

‘Shaking’ as well as fluid-ization tend to cause ‘fractioning’ of the particulate.

Maybe ‘flotation’?

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loganPosted on 30/07/2015 at 04:30

Maybe, as Robin suggested, ‘skating’? That scenario is not so extreme. Terraces [as defined in this paper] seems to suggest a kind of ‘abrasive’ skating. Requires of liquid lubricant only at points of contact at bottom of flow.

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loganPosted on 30/07/2015 at 04:48

‘Lubricant’ could be provided by the substrate, not by the relatively depleted transiting particulate.

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loganPosted on 30/07/2015 at 19:23

TThe less coarse and angular, the more boulder-ish and rounder the particulate IS, also the easier for it to transit on ‘shaking’ and to show fluid behavior.

That is beautifully showed at left bottom of first graph in this great Emily’s entry:

Coarse-ness and maximum gravitational slope directly correlated to gravitational hight. Very important document.

Really amazing!

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loganPosted on 30/07/2015 at 20:49

If looking for before/after differences when coming back to near orbits, would bet for high gravitational slopes, and cliffs near them.

Bottom of basin seems to be on consolidation process. Avalanches [and new fail lines] only if gravitational map change significantly.

Personal impression is that at Inmhotep, geology of gravitational heights is massively different to that of low lands.

Liquid speculations are quite probably about low lands, of basins…

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loganPosted on 30/07/2015 at 21:23

The consolidating Imhotep central plains should be ‘distilling’ a lot of salt at each day/night cycle, as they get warmed.

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loganPosted on 01/08/2015 at 00:45

Liquids not in a Katrina’s sense, but as difference between wet and dry wood. As in cloths in wet or dry months. As _inside a submarine entering cold waters. Something stirring around a corner down in the basement. Some drips here an there. As that spoiled old flour in the kitchen, or this progressively consolidated ancient sugar.

Extend this images, on pause, on play, for eons.

67P is a lot more active than this. Before/after in just a perihelion is going to be maximum.

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ClaudiaPosted on 07/09/2015 at 16:30

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